An arc-fault in a photovoltaic array is an undesirable occurrence where an arc of current is established between two or more conductors, causing a discharge of electricity which may cause a fire. An arc-fault can occur in the photovoltaic array, for example, because of corrosion or issues in installation.
One type of arc-fault is referred to as a series arc-fault. A series arc-fault is created when there is a discontinuity in a conductor and current bridges this gap. A series arc-fault is de-energized by opening the circuit.
Another type of arc-fault is referred to as a parallel arc-fault. A parallel arc-fault is created when an arc is established between conductors at different potentials. For example, an arc between a negative DC cable and a positive DC cable is a parallel arc-fault. In another example, an arc between conductors on different photovoltaic strings at different potentials is a parallel arc-fault. In a further example, an arc within a string where a short circuit occurs, such as in a junction box, is a parallel arc-fault. In contrast to the manner in which a series type arc-fault is de-energized, opening the circuit does not de-energize a parallel type arc-fault. Moreover, attempting to de-energize a parallel arc-fault by opening the circuit can worsen the arc, raising the risk of electrical fire. Parallel arc-faults are mitigated by either (a) shorting the string or array, or (b) by segmenting the array to safe operating voltages where the arc-fault plasma stream becomes unstable and collapses.
The NATIONAL ELECTRICAL CODE is a standard that sets forth safe installation of electrical wiring and equipment in the United States of America. In the 2011 and 2014 versions of the NATIONAL ELECTRICAL CODE, Section 690.11 requires photovoltaic direct current (DC) series arc-fault protection, but does not require parallel arc-fault protection. Accordingly, arc-fault detectors exist in the status quo that detect arc-faults, but these detectors do not differentiate between a series arc-fault and a parallel arc-fault. In addition, arc-fault detectors detect arc-faults regardless of whether they are series or parallel arc-faults. Furthermore, because existing arc-fault detectors do not specify what type of arc-fault is present, a parallel type arc-fault that is detected is simply identified as an arc-fault without regard to type. Seeing as the manner of extinguishing an arc-fault will be to open the circuit, not only does this action not extinguish the parallel arc-fault, but worsens the arc, potentially causing a fire.
It is important for arc-fault detectors to be reliable and accurate as an essential step for minimizing the risk of electrical fire.